This invention relates to a single-lens reflex camera whose lens is interchangeable, and more particularly to a system which optimally performs an autofocus control operation depending on the performance in combination of a camera body and a photographic lens being mounted.
To date, single-lens reflex cameras which are equipped with autofocus (AF) functions have been employed.
The single-lens reflex camera is a camera, to which a lens is interchangeably mounted. Since it requires a precise focusing adjustment, a method in which the amount of defocus is detected by the state of an image formed by light which passes through a lens, i.e., the so-called TTL (Through-The-Lens) type focus detection method, has been widely employed in AF (Automatic Focusing) operations.
When this method is used, a light reception device for AF operation is positioned in the body of the camera, and the elements to be driven are positioned in the lens unit. Thus, AF operation is performed by connecting the lens unit and the camera body mechanically or electrically together.
In the former case, (i.e., mechanical connection, a structure where the lens unit is equipped with only a drive force transmitting mechanism) and an AF motor provided in the camera body is used to drive the lens. In the latter case, a structure where the lens unit is equipped with an AF motor which turns on/off a motor in the camera body so as to perform a focusing operation, is used.
However, in the systems described above, the nonlinearity between the defocus amount and the amount of driving of the lens cannot be properly compensated for, because the conversion from the defocus amount into the number of pulses is conducted in a control circuit in the body. Thus, there was a problem where an optimum AF control corresponding to each interchangeable lens could not be performed.
In addition, in a structure where AF control and zoom lens driving are carried out with motors in a lens unit, since the items to be controlled in the lens unit increase, the computing capacity required for the body accordingly increases, resulting in increasing the computating load to the camera body.
Where functions of the photographic lens units are increased, it is desired for individual photographic lens units to have data processing capacity therein.